Improvement in countersinks



COUNTERSINKS. No. 186,513. Patente'dJanfZSQ1877.

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UNITED STATES PATENT CFFICEE.

DUMMER ADAMSQ OF KITTERY, MAINE.

IMPROVEMENT IN coun'reasmus.

Specification forming part o f Letters Patent No. ll-Sfijlii, datedJanuary 23, 18 77 application filed January 5, 1877.

To all whom it may concern lowing is a full and clear description:

This invention relates to that classof tools used for forming conicalseats for screw-heads, of which there are in use two classes, viz: thoseformed like a common drill, with two cuttingedges on opposite \sides ofthe axis, and no intermediate points of bearing againstthe surface beingacted upon; and those known as burrs, consisting of a conical head,serrated, and presenting a large number of cutting-edges, but no otherpoints of contact with the surface being acted upon. The first varietyis operated with least power, but has the disadvantage of slight chatteror spring, and corresponding inaccuracy. When dulled, the form andcutting-edges are easily renewed. The second variety require aconsiderable expenditure of power, because so many cutting-edges are inaction at the same time, and, when dulled, considerable labor isrequired to efiect a resharpening. These burr-countersinks possess themerit of accuracy, because of the large number of points of support.

My invention combines the merits of both varieties above described, butdispenses with the defects of both.

Itconsists in a countersink with an adjustable bit, whereby the depth ofcut may be regulated, and the bit removed for sharpening, and astationary conical head to bear upon the surface of the countersink,whereby there are but two cutting-edges on opposite sides of the axis ofrotation, and consequently all the facility of sharpening, 850., and abearing-surface, to prevent chatter andsecure ac- A is the shaft of mycountersink, and may be provided with a head fitted to an ordinary bitstock, or itmay be otherwise fitted to a mandrel or other operativemechanism. At the opposite end is the cylindrical head a, with a conicalpoint. This cylindrical head is slotted longitudinally, to receive thebit B, which is kept accurately in place by means of a screw, 06, whichpasses through said shaft A, and through a slot in the said bit. Thelower endof the bit B is bifurcated, and the shaft A rests in saidbifurcation, as shown, so, that, while the bit may move endwise, it isprevented from moving laterally. The shaft A is provided with ascrew-thread and a nut, E, which traverses thereon, todrive the bit Bforward, when desired, and to sustain it against the pressureencountered during use. The forward end of the nut E is cupped, so as toreceive within its periphery the lower ends of the bit B, toprevent'them from springing aside on account of pressure against thepoint of said bit.

By this simple arrangement I adapt my bit to use either in wood ormetal,though it is particularly adapted to the latter.

Clearance-ways e are filed in each side of the conical point of the heada, parallel with, and immediately in front of, the cutting-edges of thebit B.

When in use, the bit is so set that its outting-edges project beyond theconical surface a a distance just equal to the practicable depth of cut.The forward pressure is then sustained by the conical part of the heada, instead of upon the cutting-edges, and the latter are not subjectedto any strain or pressure except that incident to the operation ofcutting. This secures a smooth out without chatter, and symmetrical inform. Todrive' this countersink requires no more power than to drive anordinary flat drill.

The bit B may be readily sharpened without removal from the head a, itbeing only necessary to loosen the screw (1 and advance the edges beyondthe conical part of a, so that it may be applied to a grindstone.

The screwd unites the separated parts of the head a, and clamps themagainst the sides of the bit B, so as to keep the same firmly in place.When worn out, said bit may be replaced by a new one. 1

Having described my invention, What I claim as new is- L A countersinkprovided with a slit conical head, a, and aslit bit, B, longitudinallyadjustable in said head. and a transverse binding-screw, 01,substantially as set forth.

2. A shaft, A, with an external screw-thread and nut, E, and providedwith a slit conical head, combined with a slit movable bit, B,adjustable longitudinally by the operation of said nut E, substantiallyas set forth.

3. A countersink having a shaft,'A, adapted to be attached to anordinary bit-stock, lathechuck, or other suitable driving apparatus, anexternal screw, and a nut, E, thereon, a slit conical head, a, withclearance-ways e, a slit movable bit, B, and a transverse bindingscrew,d, as set forth.

DUMMER J. ADAMS.

Witnesses I I JOHN WENTWORTH, ENIN 1. WILSON.

